On 26 August 2013, Cunliffe announced a second leadership bid after David Shearer's departure from the leadership and was elected leader on 15 September 2013. Following Labour's defeat at the general election in September 2014, he resigned as leader of the Labour Party[3] and initially contested the subsequent leadership election. However he then withdrew his nomination for the leadership election before the process started.

In the 2002–2005 Parliament he held the ICT portfolios and was Associate Minister of Finance and Revenue, after previously serving as Parliamentary Private Secretary for Finance and Commerce.

During his first term (1999–2002) he served as Chair of the Commerce Select Committee, and sat on the Finance and Expenditure and Regulations Review select committees.

In 2006, in his previous role as Immigration Minister, he announced a major review of the Immigration Act 1987.[9] As Minister for Communications and Information Technology he announced local loop unbundling in the telecommunications sector.[10]

In May 2006 Cunliffe was referred to the Securities Commission by the NZX for prematurely exposing information on Telecom's future dividend plans,[11] causing Telecom's stock price to drop.

In February 2008, as the Minister of Health, Cunliffe dismissed the Hawke's BayDistrict Health Board over political, monetary and conflict of interest troubles.[14]Napier Mayor Barbara Arnott and a number of members of the district voiced opposition to Cunliffe's move as many of the board members were democratically elected.[15] Following the release of a Health Ministry-commissioned independent report into the matter, Cunliffe referred to the board as "nasty little nest of self-perpetuating provincial elites".[16]

After the 2008 general election defeat of the Labour Party, Cunliffe was made Labour's spokesman for Finance, shadowing National's Finance Minister, Bill English. Cunliffe had been touted as a future leader of the party, and party insiders had suggested he seriously considered challenging Phil Goff as leader in the aftermath of the 2008 election. Speculation of a leadership challenge again arose during the June 2010 expenses scandal and again after the "Cartergate" affair.

In November 2012 during a Labour Party conference, there was much media speculation Cunliffe would launch a challenge against David Shearer for leadership of the party.[18] On the morning of 19 November, Cunliffe confirmed he was not challenging Shearer, and would indeed back him if a vote was taken.[19] Labour Chief Whip Chris Hipkins publicly refuted that Cunliffe had not been making a bid for the leadership over the conference weekend, and stated that fellow caucus members were frustrated with Cunliffe's behaviour.[20]

On 20 November 2012, Shearer sacked Cunliffe as economic development spokesman, and demoted him to the back bench, citing Cunliffe's inability to express his support for Shearer's leadership at the Labour Party Conference. Cunliffe denied that he had been disloyal. Cunliffe was left with no spokesmanships.[21] In February 2013 Shearer reshuffled his caucus lineup. Cunliffe was given the Revenue portfolio, but was not promoted back into the shadow cabinet.[22]

On 22 August 2013, Shearer announced his resignation as leader of the Labour Party, fuelling speculation that Cunliffe would make another bid for the leadership. Cunliffe did not confirm his candidacy immediately, saying to the press in Parliament that same day: "I am going to be taking the next few days to consult with my family, with colleagues and with party supporters and I won't be making a decision until after I have done that."[23] Victoria University of Wellington's iPredict online predictions market showed the probability of Cunliffe becoming the next leader of the Labour Party at 66%, compared to under 26% support for Shearer's deputy Grant Robertson, social development spokesperson Jacinda Ardern was at 5%, and list MP and former union leader Andrew Little was on 2%.[24]

Cunliffe formally entered the 2013 New Zealand Labour Party leadership election during a press conference in his New Lynn electorate office, saying he had consulted colleagues, supporters, and family and had been "humbled by the response."[25] He also said they had expressed confidence in his ability to "bring together a party and a government that provides a strong, clear voice for fairness, inclusion, and prosperity to be shared by all."[26] His announcement came in the wake of a ONE News Colmar Brunton poll released by the current affair program Q+A which showed Cunliffe winning the support of 29% of the eligible voters asked, and 32% of those polled who support Labour. Challengers Shane Jones and Grant Robertson are on 11% and 10%, respectively.[27] After the first public Labour Party leadership selection process in New Zealand history, Cunliffe was elected leader on 15 September 2013.[28] He won with the support of 32% of the Labour Party caucus, 60% of Labour Party members, and 70% of affiliated unions.[29]

Cunliffe is a supporter of a New Zealand republic. During the Address-In-Reply debate on 4 September 2002, Cunliffe said: "A New Zealand where we journey together towards maturity as a nation, and to the Commonwealth republic I personally believe we will become before the Treaty turns 200".[33]

Cunliffe married prominent Auckland lawyer Karen Price when he was 21 and she was 19. They had two sons, and lived in the Auckland suburb of Herne Bay.[5] They separated in 2015.[1] Cunliffe's father Bill was born in Ngahere in 1915 and worked at the railways. His great-grandfather, William Cunliffe, married Phoebe Seddon, the elder sister of Richard Seddon, who would later become known as 'King Dick'. Seddon, New Zealand's longest serving prime minister, was thus Cunliffe's great-(great-)uncle.[34]

Cunliffe is the son of an Anglican minister, and was raised in the Church of England. He has described himself as a "liberal Anglican," and an "infrequent attender of church, but it's a big part of my life."[35] He attends St Matthew's Anglican Church in Auckland, and is a supporter of the Auckland City Mission.